Portable transceiver are becoming ever smaller and lighter. Mobile phones, which are typical wireless terminals subject to this trend, offer a widening range of services for data communications, such as text and video transmissions, in addition to voice communications. Accordingly, the performance of the antenna, which is used for transmitting and receiving radio waves, and inputting and outputting signals, is one factor affecting the performance of mobile phones.
In the field of mobile phones, a single antenna that can receive and transmit signals via multiple radio frequencies at high sensitivity is highly demanded.
A conventional antenna for portable cellular telephone installed in a mobile phone is described next with reference to FIG. 9.
FIG. 9 is a schematic view of the mobile phone in which the conventional antenna for portable cellular telephone is installed. As shown in FIG. 9, portable transceiver antenna 3 is disposed in parallel to ground plane 8. This portable transceiver antenna 3 includes first antenna element 1 that resonates at a first radio frequency and second antenna element 2 that resonates at a second radio frequency. In wireless terminal 9, portable transceiver antenna 3 is coupled to feeding point 4 provided on ground plane 8, and then to radio circuit 7 via matching circuit 5 and transmission line 6.
Accordingly, conventional portable transceiver antenna 3 is configured to receive power from one common feeding point 4 for both first antenna element 1 and second antenna element 2. In the following description, first antenna element 1 resonates at GSM (Global System for Mobile communication: 880˜920 MHz) frequencies and second antenna element 2 resonates at DCS (Digital Cellular System: 1,100˜1,880 MHz) frequencies, frequencies higher than those for first antenna element 1.
For receiving GSM radio frequencies, in the above structure, the current induced by the radio waves received by first antenna element 1 is transmitted from feeding point 4 to radio circuit 7 via matching circuit 5 and transmission line 6 so as to receive a predetermined signal.
For transmitting GSM radio frequencies, a predetermined signal generated at radio circuit 7 is sent from transmission line 6 to first antenna element 1 via matching circuit 5 and feeding point 4. This signal is then induced in first antenna element 1 and emitted as radio waves.
Also for DCS, radio waves are conventionally transmitted and received at second antenna element 2 via single feeding point 4 in the same way as for GSM.
In the conventional antenna for portable cellular telephone, however, resonance frequencies in two significantly different ranges cannot readily be independently and efficiently adjusted because the conventional antenna is configured to feed power to first antenna element 1 and second antenna element 2 from one feeding point 4. In addition, matching circuit 5 for gaining two different resonance frequencies of GSM and DCS is also shared.
One of the prior arts related to the present invention is disclosed in the Japanese Patent Laid-open Application No. 2003-101335.